Cranking Voltage Drop Test

[whittlebeast]

There has been a fair amount of conversation lately on the net regarding grounding. I just did a quick test.

https://youtu.be/h8kURPiewyY

Andy

[M30guy]

what are you proving here?

[whittlebeast]

At this point, I am questioning what is the best way to advise people to run grounding. The problem is the voltage drop at high amperage all adds up.

[billr]

That drop to 10V is pretty common/normal, and causes no problem by itself. Have you scoped the battery terminals directly? I think a certain amount of voltage drop is internal resistance of the battery itself, no amount of extra copper in the wiring will reduce that.

[jsmcortina]

It's the noise in the ground that is of interest.

James

[Blown88GT]

Without knowing how & where the scope is connected, can only say this about the noise.
It looks like the scope probe ground is floating.

[whittlebeast]

The ground of the scope was clipped to a clean valve cover bolt. The positive of the scope was jumpered back to the positive terminal of the battery that sits in the passenger seat area. On the second test the remote probe was moved to the negative post of the battery. In the last test, the remote probe was moved to the chassis ground that I have on the firewall (inside the car) that is also where I ground the motor and MS3 Pro Ultimate.

My ECU is actually powered by a fairly high dollar power supply that converts whatever the batter volts is to a regulated 14 volts.

You can see it in this video.

https://www.youtube.com/watch?v=0cjLHZNspJ8

Andy

[Blown88GT]

...the chassis ground that I have on the firewall (inside the car) that is also where I ground the motor and MS3 Pro Ultimate.
...My ECU is actually powered by a fairly high dollar power supply that converts whatever the batter volts is to a regulated 14 volts...

For your hardware, a battery ground has to be made at the firewall, too.
The firewall tie point is your single point ground.
Ford did the same sort of thing with the EEC-IV on the Mustang. The ECU had an additional ground back to the car's chassis.
The psu should have isolated power & ground, but you never know for sure.
Is the psu chassis internally isolated from ground? You have isolated it on rubber standoffs.
I suspect a ground loop in the vehicle and/or another one caused by the scope probe ground.
Is any device on the vehicle, such as a battery charger, connected to AC power besides the scope?
Why do you need the psu?

[whittlebeast]

That car is an 1800# car (2008# with me in it). Anything you can do to avoid adding weight is an advantage. An added ground wire weighs something. Parts not installed will never fail and weigh nothing.

Regarding the power supply, It weighs less than an alternator. If the alternator was there, it needs to run about 3 times the the RPM of the motor. The motor accelerates at about 3000 RPM per sec on course, so an alternator would need to accel at 9000 RPM per sec. On a throttle stab, I get to about 9000 RPM per sec at the crank. Last, the power supply was cheaper than an alternator and with all the effort to build mounts, voltage regulators let alone finding a place to mount it.

The ECU is rubber mounted and the case is not separately grounded. The power supply is also rudder mounted and as I recall, it is not grounded.

Andy